Immune response and gene expression of white shrimp (Litopenaeus vannamei) induced by microbial immunostimulants

A 26-day bioassay was performed to evaluate the immunostimulating effect of lactic acid bacteria and yeasts (IM), added in the feed, in Litopenaeus vannamei. Bioassay treatments were performed in triplicate: I) control diet (Camaronina (R)); II) IM in food, daily; III) IM in food every three days and; IV) IM in food every six days. The shrimp were WSSV-free. To study the immune system, a total count of hemocytes, the concentration of superoxide anion, and the phenoloxidase activity were analyzed. We also studied the semiquantitative expression of six immune system genes, using the technique of RT-PCR. There was no significant increase in the growth and survival, the total count of hemocytes, the protein concentration, and the concentration of superoxide anion. Phenoloxidase activity in plasma in the treatment IV was significantly higher than in treatments I, II, and III. The phenoloxidase of HLS (proPO) in the IV treatment was significantly higher than in treatments I and III. The IM caused a significant overexpression of the genes coding for the prophenoloxidase (treatment IV), lysozyme (treatment III), and transglutaminase (treatment II) relative to the untreated animals (control). The mixture of microbial immunostimulants may increase the resistance of cultured L. vannamei against pathogens.